The present invention relates to a biscompatible flexible tubular device for insertion into the body during medical procedures. More particularly, the invention relates to flexible tubular devices for use as catheters, including guide catheters and balloon catheters, guidewires, catheter sheaths, catheter introducers, drug infusion catheters/guidewires, and methods for making the same.
Catheters and Guidewires
Catheters are relatively thin and flexible tubes used in the medical field for numerous applications. Catheters are made by any number of different methods and designs. However, in most catheter designs it is desirable to obtain a maximum torsional rigidity while retaining a satisfactory longitudinal flexibility and stiffness without kinking. These features will allow the orientation of the catheter to be manipulated so that the catheter can be guided through small body vessels and cavities. These features will also prevent any kinking from occurring, and provide the catheter with enough "push" or stiffness so as to prevent the catheter from wrinkling or folding back on itself during this process. The specific nature of these characteristics will of course vary depending on the specific application for which the catheter is being used. Yet another consideration is that a relatively small outside diameter must be maintained while providing a lumen or an inside diameter as large as possible.
Guide wires require the same general type of characteristics. However, with guide wires it is important to minimize the outside diameter of the guide wire so that they will readily fit inside of the lumen of the catheter.
Catheters and guide wires are used both as diagnostic tools and in the treatment of diseases. One such diagnostic procedure is cardiac catheterization which is a widely performed procedure, being used for assessment of coronary artery disease. Other uses are neurologic uses, radiologic uses, electrophysiologic uses, peripheral vascular uses, etc. One example of a treatment use is the use of balloon catheters in dilation procedures to treat coronary disease. Dilation procedures rely upon the use of a catheter for injection of contrast and delivery of guidewires and dilation catheters to the coronary artery or other arteries. An example of the use of guide wires is for Percutaneous Transluminal Coronary Angioplasty (PTCA) balloons and for guiding diagnostic catheters through the arteries and to body organs.
The catheters and guide wires used in these and other procedures must have excellent torque characteristics, and must have the requisite flexibility. In addition, it is important that catheters and guidewires provide sufficient longitudinal support for "pushing" of items through the arteries and other vessels such as when feeding the balloon portion of an angioplasty catheter through the arteries. Unless there is sufficient stiffness, the catheter or guidewire will wrinkle or fold back on itself.
Typically, in the case of a catheter, the larger the ratio of inside to outside diameter, the better. For guide wires it is important to maintain a small outside diameter. Smaller catheter and guidewire outside diameter sizes result in less chance of arterial damage.
Catheters and guide wires must have sufficient torque such that they do not buckle when being manipulated. Finally, flexibility is important so that the catheter or guide wire can be manipulated into the varying arterial branches encountered by the catheter. The guide wire must resist being inadvertently kinked as this results in loss of torque control.
Prior art catheters are typically made of flexible materials which are reinforced such that the resulting composite catheter approximates the desired characteristics. In alternative approaches, guide wires are used in conjunction with catheters to assist in manipulating and moving the catheters through the arterial system in the body.
U.S. Pat. No. 4,020,829 to Willson et al. discloses a spring guide wire for use in catheterization of blood vessels. The guide wire is axially slidable within a thin walled, flexible plastic catheter. The distal portion of the guide wire is of a relatively short length and is connected to a relatively long, manipulative section capable of transmitting rotational torque along its length. In this invention the catheter tube might be advanced over the guide wire after the guide wire has been properly positioned or the catheter might be advanced together with the guide wire, the guide wire providing a reinforcement for the thin wall of the catheter.
U.S. Pat. No. 4,764,324 to Burnham discloses a method for making a catheter. In Burnham, a reinforcing member is heated and applied to a thermoplastic catheter body so as to become embedded in the wall of the catheter. The wall of the catheter is then smoothed and sized so as to produce a composite, reinforced catheter.
The art of applying braiding or multi-pass wire reinforcement to a catheter inner core is also well developed and machinery for performing such a step is well known. Typically, such reinforcement material is applied to the inner core tube of the catheter in a pattern of overlapping right and left hand helices. The braiding process usually requires that the machinery performing the braiding process to move the reinforcement material alternately radially inwardly and outwardly, as well as circularly, whereby the tension of the reinforcement material continuously varies. This varying tension can result in the reinforcement material breaking particularly as the speed of braiding increases. Yet another problem with braided catheters is that their inside diameter is relatively small compared to their outside diameter. The braids are quite loose also.
Current catheters often suffer from either problems of torque, size, flexibility, kinking, and poor support during PTCA in the case of guide catheters. Moreover, catheters cannot be readily made with variable stiffness along the length of the catheter.
Catheter Sheaths and Introducers
Catheter sheaths and introducers are used to provide a conduit for introducing catheters, fluids or other medical devices into blood vessels. A catheter introducer typically comprises a tubular catheter sheath, a hub attached to the proximal end of the sheath having hemostasis valve means to control bleeding and to prevent air embolisms, and a removable hollow dilator that is inserted through the hub, valve means and the lumen of the catheter sheath. Many catheter introducers also contain a feed tube that is connected to the hub to facilitate the introduction of fluids into the blood vessel.
The procedure for positioning the introducer into a blood vessel begins by inserting a hollow needle through the skin and into the lumen of the desired blood vessel. A guidewire is then passed through the needle and into the blood vessel. The needle is then removed leaving the guidewire in the vessel. Next, the sheath and dilator are advanced together over the guidewire until the distal ends of the dilator and sheath are positioned within the lumen of the vessel. The guidewire and dilator are then removed, leaving the distal end of the sheath within the vessel. Catheters or other medical devices can then be passed through the introducer and sheath into the desired vessel.
Conventional sheaths are made of plastic and as shown in FIG. 14, are subject to kinking if bent without internal support. This kinking can occur during the insertion of the device or if the patient moves while the sheath is in the vessel. Unfortunately, this kinking can create sharp edges or irregularities in the sheath that can damage blood vessel linings. This kinking can also make the introduction of devices or fluids more difficult and can cause patient bleeding problems around the sheath tubing. Therefore, there arises a need for a catheter introducer with a catheter sheath that is flexible and resistant to kinking.
Conventional catheter sheaths also have a limited hoop strength making them susceptible to burring or notching. This burring and notching can occur during the insertion of the sheath and dilator into the blood vessel or if the forces exerted on the sheath cause it to become noncircular. These burrs and notches can also damage blood vessel linings. Therefore, there arises the need for a catheter sheath that has sufficient hoop strength to prevent deformation in the sheath to resist the formation of burrs or notches.
It is also important that the sheath have a minimum thickness to reduce the size of the puncture hole in the blood vessel. Larger puncture holes make hemostasis more difficult upon removal of the sheath. The sheath should also be lubricous to make the insertion and extraction of the sheath and other devices easy. Therefore, there arises the need for a catheter sheath for use with a catheter introducer that has a thin wall, that is flexible and resistant to kinking, that is lubricous, and that has sufficient hoop strength to prevent the catheter sheath from burring or notching.
One method for creating a sheath that may meet the above requirements would be to make the sheath from expanded polytetrafluoroethylene (PTFE) as disclosed in U.S. Pat. No. 5,066,285. While PTFE is more flexible and has a higher hoop strength than the plastics used in conventional sheaths, it is still a plastic-type material that may be subject to the same deformation problems.
Drug Infusion Catheters/Guidewires
Drug infusion catheters/guidewires are devices that act like both catheters and guidewires and are capable of delivering drugs or other fluids to a specific location within a patient's blood vessel such as an occluded blood vessel. The guidewire type devices are typically comprised of a coil spring with a heat shrunk TEFLON.RTM. coating and a core wire that can be inserted and removed from the lumen in the coil spring. The coated coil also contains either side holes or an end hole or a combination thereof in its distal end to enable the drugs or other fluids to be sprayed into the blood vessel.
During use, the coated coil spring and its core wire are advanced together through the patient's circulatory system much like conventional guidewires. Upon reaching the desired location, the core wire is removed creating a small catheter like device. Drugs or other fluids are pumped through the lumen in the coated coiled spring, out of the holes and into the blood vessel at the desired location.
Because these devices act like guidewires, the outside diameter of the devices, and therefore the lumen, are limited in size. Therefore, a second type of drug infusion catheter/guidewire device utilizes a catheter like member with side holes and a tapered distal end having an end hole generally equal to the outside diameter of a guidewire. These catheter type drug infusion catheter/guidewire devices are advanced over a guidewire to the desired location and then drugs are then pumped through and out of the holes in the catheter like member. These devices can also be used in combination with the guidewire type drug infusion devices.
As described above, drug infusion catheter/guidewire devices act like both catheters and guidewires. Therefore, these devices must have the same characteristics as catheters and guidewires. These devices must obtain a maximum torsional rigidity while retaining a satisfactory longitudinal flexibility and stiffness without kinking. They must also maintain a small outside diameter while providing a lumen as large as possible.